Metal roof structures typically comprise a series of parallel rafter beams extending across the building in one direction and purlin beams parallel to each other mounted on top of the rafters extending in a direction normal to the rafters. Insulation material in long sheets is placed in the area between purlins. The sheets of insulation material can be laid along the length of the purlins or across the purlins in a direction normal to the purlins. If desired, the roof structure can have a first layer of insulation material which is laid along the length of the purlins, and a second layer of insulation material which is laid laterally across the purlins on top of the first layer on insulation. Hard roofing material such as metal decking is then attached on top of the purlins over the insulation material. Because the hard roofing material comes in long sheets and the roofs generally have two sloped sections, it is customary to construct the roof along the length of the structure from one end to the other. The workers stand on the previously laid section of roof to construct the next section.
The insulation material must be supported between the purlins beneath the hard roofing material. Various methods of supporting the insulation material have been used. Mounting straps or wire mesh which are attached to or draped over the purlins forming a lattice have been used. This is referred to as banding. A sheet, typically made of vinyl and acting as a vapor barrier, is then rolled onto the lattice, and insulation material is placed between adjacent purlins and over the sheet. If the installation of the lattice is done from underneath the roof structure, scaffolding or lifting equipment is typically required for installation. Since the lattice encompasses the entire roof, installation is costly and time consuming. Once the hard roofing material is mounted on the purlins, the sheet can support the insulation material and the lattice no longer serves any useful purpose.
Some systems dispense with the lattice and use the sheet itself to support the insulation material. The support sheet is draped from the adjacent purlins and the insulation material is placed on top of the support sheet. A carriage has been used to aid in the dispensing of the support sheet. The carriage is positioned on top of the purlins and travels the length of the purlins during the roof construction. A roll of the support sheet material is mounted on the carriage and the support sheet is dispensed from the roll and placed on top of the purlins. As the carriage travels the length of the purlins, the support sheet is draped across the purlins. However, the support sheet sags between the purlins and results in a small vertical height at the sides of the insulation cavity adjacent to the purlins, and results in a compression of the insulation material in that area.
An additional step to compensate for the small vertical height when draping the insulation material is to use clips to hold the support sheet onto the purlin to reduce sagging. Clips that are attached to the bottom of the purlins require installation from underneath the roof structure and typically require scaffolding or lifting equipment. Clips that are installed over the purlins and extend the support sheet downward are known in the art but require the workers to lean over the edge of the previously laid section of roof and attach the clip to the purlin. Because of the increased costs due to the expense of the installation and the clips themselves, the use of clips is undesirable.
Guides have been used to prevent the sagging of the support sheet and increase the vertical height at the sides of the insulation cavity adjacent to the purlins. The guides are mounted on the carriage and extend downward on top of the sheet. The guides are positioned near the purlins so that the sides of the sheet extend downward. This causes the sheet to create a generally rectangular cross-sectional area into which the insulation material can be placed. The guides, however, can tear up the sheet as the carriage moves along the length of the purlins. Also, because the guides must force the sheet downward, the longitudinal edges of the sheet can be misaligned with the tops of the purlins. The edges of the sheet must then be re-aligned so that when the hard roofing material is attached to the tops of the purlins, the sheet supports the insulation. This misalignment also exposes the edges of the sheet, thereby creating an undesirable appearance when the roof structure is viewed from below.
It would be desirable to have a system of building a roof structure which is inexpensive and simple to construct and which does not require the use of lattice straps, clips, or guides, yet provides for an insulation support system which enables the full thickness of the insulation blanket to be used.